When drilling oil and gas wells, it is frequently desirable to ream a borehole that has been initially created by a drill bit or other cutting tool. This reaming can remove any projections that may have been missed by the first pass of the drilling assembly, creating a more uniform borehole. In addition, a reamer may be used to enlarge a borehole (e.g., below a casing shoe), allowing, for example, the installation of additional casing strings.
However, since optimum reamers often cannot be used until they have passed through a first cased section of the borehole, additional obstructions often remain inside the casing that prevent or hinder the installation of additional downhole casing strings. In the past, material in the first casing was removed through the use of a separate, dedicated drill-out, requiring additional time and expense. Alternatively, reamers that were less than optimally-sized for use with a corresponding drill bit were employed. These approaches may reduce the stability of the drilling assembly, which may result in more vibrations and drilling inefficiency.